1. Field of the Invention
The present invention relates to a metal fastening member such as a T nut, a rivet and the like or to an outer casing member for a bullet having a hollow shaft portion. More specifically, the present invention relates to a metal fastening member and an outer casing member for a bullet having such a structure in that a cap provided at a tip end portion is easily separated to come off when driven into an object.
2. Description of the Background Art
A conventional T nut having a thin flarable portion (prospective caulked portion) in the shaft portion is disclosed, for example, in U.S. Pat. Nos. 5,238,344 or 5,348,432.
A T nut 11 described in U.S. Pat. No. 5,238,344 has such a shape as shown in FIGS. 95A and 95B, which is provided as an integral part by sheet metal working of an iron based metal plate, for example, which T nut includes a shaft portion 12 and a flange portion 13 protruding outward from a first end portion of the shaft portion 12.
Shaft portion 12 has a hollow cylindrical shape with uniform outer diameter, a flarable portion 14 at a second end portion opposite to the first end portion, and a female screw 15a formed on an inner peripheral surface of a female screw forming portion 15 other than the flarable portion 14. Flarable portion 14 is made thinner in thickness as compared with female screw forming portion 15. Therefore, when female screw 15a is to be formed, the thread can be formed either from the side of the first end portion or the second end portion of the shaft portion 12.
Flange portion 13 has two pawls 16 formed by mushing part of an outer peripheral edge of flange portion 13 from the outer side to the inner side, which pawls oppose to each other at 180xc2x0, protruding toward the second end portion of shaft portion 12. As a result of formation of the pawls 16, notches 17 having approximately semi circular cross section are left at the outer peripheral edge of flange portion 13.
Such a T nut 11 is used, for example, in the manner as shown in FIG. 97A. Referring to FIG. 97A, shaft portion 12 is first inserted to an object 19 of fixing formed of resin material or wood and having a receiving hole 18 formed in advance, and in this state, the flarable portion 14 is caulked by a caulker, so that a caulked portion 14a is formed on one surface side of object 19 of fixing. At the same time, pawls 16 are driven into the other surface of the object 19 of fixing. Thus T nut 11 is completely fixed in object 19.
A T nut 31 described in U.S. Pat. No. 5,348,432 has such a shape as shown in FIGS. 96A and 96B. Similar to T nut 11 described above, it is provided as an integral body by sheet metal working of an iron based metal plate, for example, and the T nut has a shaft portion 32 and a flange portion 33 protruding outward from the first end portion of shaft portion 32. The shaft portion 32 has a female screw forming portion 35 where a female screw 36 is formed on the inner periphery, and the T nut also has a flarable portion (prospective caulked portion) 34. The structure of T nut 31 is different from that of T nut 11 in that two pairs of pawls 37 and 38 as well as 39 and 40 extending from the first end portion toward the second end portion are arranged opposing in the radial direction of flange portion 33, so that flange portion 33 as a whole has substantially octagonal shape.
Such a T nut 31 is generally called a xe2x80x9chopper feed T nutxe2x80x9d, since the T nut 31 can be smoothly moved along a feed track which is provided on a nut fixer for fixing the nut to the object, enabling automatic feeding of the T nuts. For example, British Patent No. 1,157,734 describes a type of such a hopper feed T nut in detail.
FIG. 96B shows the aforementioned feed track 243 in phantom lines. Feed track 243 includes a pair of guide rails 244 and 245 having C-shaped sections, which are symmetrically arranged to be opposite to each other. Flange portion 33 is received by each of the guide rails 244 and 245, so that T nut 31 is moved along feed track 243 in a prescribed posture while locating the pawls 37 to 40 between the guide rails 244 and 245. Though not shown, feed track 243 is frequently bent to bring the T nut 31 into a desired posture, so that shaft portion 32 is aligned with a hole provided in an object, not shown.
T nut 31 is used in the similar manner as T nut 11, as shown in FIG. 97B, for example. More specifically, shaft portion 32 of T nut 31 is inserted to a through hole 18 of an object 19 of fixing, flarable portion 34 is caulked by a caulker in this state, and caulked portion 34a is formed on the side of one surface of object 19. At the same time, pawls 37 to 40 are driven into the other surface of object 19.
In such a state of fixing of T nut 31, rotation of T nut 31 relative to the object 19 of fixing is inhibited by pawl 37 to 40, and flange portion 33 and caulked portion 34a grip the object 19, so that T nut 31 is not slipped from through hole 18. Thus, T nut 31 is firmly fixed on object 19, and the fixed state is maintained semi-permanently.
When the above described T nut is to be driven to the object of fixing under automatic control, however, it is necessary to provide a receiving hole exactly at the expected position to which T nut is driven, of the object of fixing. Further, it is necessary to position the T nut exactly at the receiving hole and to drive the T nut into the object.
Therefore, when the T nut is to be driven to the object of fixing by automatic control, exact positioning is necessary both in the process of forming receiving hole and the process of driving the T nut, which results in lower efficiency of working and increase in cost of driving.
The present invention was made to solve the above described problems and its object is to provide a metal fastening member having such a structure that enables exact driving into the object of fixing without the necessity of forming a receiving hole in advance.
Another object of the present invention is to provide an outer casing member for a bullet of which tip end portion surely tears simultaneously with collision at the object.
According to an aspect, the present invention provides a metal fastening member including a cylindrical shaft portion having a flarable portion which is expected to be caulked and a shaft body portion provided continuous from the flarable portion, and a cap portion provided continuous from an end portion of the flarable portion opposite to the shaft body portion, and formed of an integral metal material, wherein a connecting region between the flarable portion and the cap portion has such a shape in that, a force bending outward the flarable portion is exerted when a pressing force is applied to the tip end surface of the cap portion in a direction from the side of the cap portion to the side of the flarable portion, so that the cap portion is separated or goes off from the flarable portion by the bending force and the flarable portion comes to be bent outward.
In the above described structure, when the metal fastening member is driven into the object of fixing, the object of fixing is removed by the cap portion, and therefore it is unnecessary to provide in advance a receiving hole for driving the metal fastening member in the object of fixing.
As an example of a preferred embodiment, a structure may be adapted in which an inner surface of the flarable portion is recessed outward at the connecting region between the flarable portion and the cap portion, so that immediately after driving the metal fastening member into the object of fixing, when the cap portion collides an abutting member provided outside, the cap portion is kept in the state colliding against the abutting member, whereas an external force for caulking is applied to the flarable portion. At this time, as the inner surface of the flarable portion is recessed outward, the external force for caulking flows outward. As a result, caulking of the flarable portion is ensured.
In order to implement the present invention in a more preferred state, the following structure may be adopted.
Preferably, in the connecting region between the flarable portion and the cap portion, the inner surface of the flarable portion is curved gradually outward, toward the cap portion.
Preferably, in the connecting region between the flarable portion and the cap portion, the flarable portion has its thickness gradually reduced outward, toward the cap portion.
Preferably, on an outer peripheral surface of the shaft portion at the connecting region between the flarable portion and the cap portion, a groove is provided extending in the peripheral direction.
By adapting the above described structures, the external force applied to the flarable portion flows outward in a preferable state and, as a result, caulking of the flarable portion can be ensured.
In another preferred embodiment, the cap portion has such a shape that has a dent in the central portion. Alternatively, the cap portion has an opening at the central portion. A female screw is provided at an end surface of the opening. Alternatively, the cap portion may have a shape that is protruded at the central portion.
In another preferred embodiment, a female screw is formed at least on a part of the inner periphery of the shaft body portion. Preferably, a flange portion protruding outward is provided at an end portion of the shaft body portion opposite to the flarable portion.
Preferably, the flange has a polygonal shape and includes, on the outer periphery of the flange, a pawl extending toward the side of the cap portion. Alternatively, the flange preferably has a polygonal shape and includes a protruded portion extending toward the side of the cap portion.
Preferably, the flange has a circular shape and includes a pawl on the outer periphery of the flange extending toward the side of the cap portion. Alternatively, the flange preferably has a circular shape and includes a protruded portion extending toward the side of the cap portion. Such a structure enables used of the metal fastening member as a T nut or a rivet.
Preferably, in an approximately annular region providing a periphery of the shaft portion on a side closer to the shaft body portion than the region which will be flared by the caulking of the flarable portion, a portion of small thickness is further provided by locally making thinner the thickness of the shaft portion, which thin portion has sufficient strength so as not to be torn by an axial force exerted in the state of use when the nut is caulked and fixed in the object and breaks when a tractive force larger than a prescribed magnitude is applied in the axial direction, separating the shaft portion into two.
Because of this structure, when a jig that exerts a tractive force in the central axial direction of the shaft portion on the portion of small thickness provided in the shaft portion is used with the fastening member caulked in the object, it becomes possible to tear the metal fastening member at this portion and to separate the member into two easily. As a result, the metal fastening member which has been fixed by the flange portion and the caulked portion gripping the object from the upper and lower surfaces can be easily removed from the object.
In a preferred embodiment, the flarable portion of the shaft portion has an inner diameter larger than the inner diameter of the shaft body portion, and has an outer diameter larger than the outer diameter of the shaft body portion.
In a preferred embodiment of the present invention, the shaft body portion of the shaft portion has an inner diameter larger than the inner diameter of the flarable portion, and an outer diameter larger than the outer diameter of the flarable portion.
The following structure may be adopted for the metal fastening member of a more preferred embodiment.
For example, the present invention provides a metal fastening member including a cylindrical shaft portion having a flarable portion which is expected to be caulked and a shaft body portion provided continuous from the flarable portion, and a flange portion extending outward to an end portion of the shaft body portion opposite to the flarable portion, and formed of an integral metal material, wherein a female screw is formed at least at a part of an inner periphery of the shaft body portion, the flange has a polygonal shape and includes a pawl on the outer periphery extending toward the side of the cap portion, the cap portion has an opening with a female screw provided on an end surface of the opening, and the connecting region between the flarable portion and the cap portion has such a shape that a force bending outward the flarable portion is exerted when a pressing force is applied to the tip end surface of the cap portion in a direction from the side of the cap portion to the side of the flarable portion, so that the cap portion goes off from the flarable portion and the flarable portion is bent outward by the bending force.
As to another preferred embodiment, the present invention provides a metal fastening member including a cylindrical shaft portion having a flarable portion which is expected to be caulked and a shaft body portion provided continuous from the flarable portion, and a flange portion extending outward to an end portion of the shaft body portion opposite to the flarable portion, and formed of an integral metal material, wherein a female screw is formed at least at a part of an inner periphery of the shaft body portion, the flange has a circular shape and includes a pawl on the outer periphery extending toward the side of the cap portion, the cap portion has an opening with a female screw provided on an end surface of the opening, and the connecting region between the flarable portion and the cap portion has such a shape that a force bending outward the flarable portion is exerted when a pressing force is applied to the tip end surface of the cap portion in a direction from the side of the cap portion to the side of the flarable portion, so that the cap portion goes off from the flarable portion and the flarable portion is bent outward by the bending force.
As a further preferred embodiment, the present invention provides a metal fastening member including a cylindrical shaft portion having a flarable portion which is expected to be caulked and a shaft body portion provided continuous from the flarable portion, and a flange portion extending outward to an end portion of the shaft body portion opposite to the flarable portion, and formed of an integral metal material, wherein the shaft body portion of the shaft portion has an inner diameter larger than the inner diameter of the flarable portion and an outer diameter larger than the outer diameter of the flarable portion, a female screw is formed at least at a part of an inner periphery of the shaft body portion, the flange has a polygonal shape and includes a pawl on the outer periphery extending toward the side of the cap portion, the cap portion has an opening with a female screw provided on an end surface of the opening, and the connecting region between the flarable portion and the cap portion has such a shape that a force bending outward the flarable portion is exerted when a pressing force is applied to the tip end surface of the cap portion in a direction from the side of the cap portion to the side of the flarable portion, so that the cap portion goes off from the flarable portion and the flarable portion is bent outward by the bending force.
As a further preferred embodiment, the present invention provides a metal fastening member including a cylindrical shaft portion having a flarable portion which is expected to be caulked and a shaft body portion provided continuous from the flarable portion, and a flange portion extending outward to an end portion of the shaft body portion opposite to the flarable portion, and formed of an integral metal material, wherein the shaft body portion of the shaft portion has an inner diameter larger than the inner diameter of the flarable portion and an outer diameter larger than the outer diameter of the flarable portion, a female screw is formed at least at a part of an inner periphery of the shaft body portion, the flange has a circular shape and includes a pawl on the outer periphery extending toward the side of the cap portion, the cap portion has an opening with a female screw provided on an end surface of the opening, and the connecting region between the flarable portion and the cap portion has such a shape that a force bending outward the flarable portion is exerted when a pressing force is applied to the tip end surface of the cap portion in a direction from the side of the cap portion to the side of the flarable portion, so that the cap portion goes off from the flarable portion and the flarable portion is bent outward by the bending force.
Preferably, a groove is provided extending in the peripheral direction on an outer peripheral surface of the shaft portion at a connecting region between the flarable portion and the cap portion.
Preferably, in the connecting region between the flarable portion and the cap portion, the inner surface of the flarable portion is provided recessed outward.
Preferably, in the connecting region between the flarable portion and the cap portion, the inner surface of the flarable portion is curved gradually outward, toward the cap portion.
Preferably, at the connecting region between the flarable portion and the cap portion, the flarable portion is provided with its thickness gradually reduced toward the cap portion.
Preferably, in an approximately annular region providing a periphery of the shaft portion on a side closer to the shaft body portion than the region which will be flared by the caulking of the flarable portion, a portion of small thickness is further provided by locally making thinner the thickness of the shaft portion, which thin portion has sufficient strength so as not to be torn by an axial force exerted in the state of use when the nut is caulked and fixed in the object and breaks when a tractive force larger than a prescribed magnitude is applied in the axial direction, separating the shaft portion into two.
More preferably, the flarable portion of the shaft portion has an inner diameter larger than the inner diameter of the shaft body portion and has an outer diameter larger than the outer diameter of the shaft body portion.
According to another aspect, the present invention provides an outer casing member for a bullet including a cylindrical shaft portion and a cap portion provided continuous from one end of the shaft portion and having a protruded central portion, formed of an integral metal material, wherein a connecting region between the shaft portion and the cap portion has such a shape in that a force bending the shaft portion outward exerts when a pressing force is applied to the tip end surface of the shaft portion in a direction from the side of the cap portion to the side of the shaft portion, so that the cap portion goes off from the shaft portion and the shaft portion is bent outward by the bending force.
When the outer casing member for a bullet having such a structure is applied to a bullet, the cap portion provided at the tip end portion is torn off, causing explosion, so that the object can effectively be broken by the explosion.
In order to implement the present invention in a preferable state, at the connecting region between the shaft portion and the cap portion, an inner surface of the shaft portion is recessed outward. Alternatively, at the connecting region between the shaft portion and the cap portion, preferably, the inner surface of the shaft portion is provided gradually curved outward toward the cap portion. Preferably, at the connecting region between the shaft portion and the cap portion, the shaft portion is provided with its thickness made thinner gradually outward, toward the cap portion. Preferably, a groove provided extending in the peripheral direction is provided on an outer peripheral surface at the connecting region between the shaft portion and the cap portion. Preferably, the cap portion has a dent in the central portion. Alternatively, a female screw is formed at least partially on an inner periphery of the shaft portion. Alternatively, a male screw is preferably formed at least partially on an outer periphery of the shaft portion.
By adapting such a structure, the cap portion provided at the tip end is surely torn, causing explosion when the outer casing member for the bullet collides against the object, and hence the object can effectively be broken by the explosion.